This invention relates in general to an apparatus and technique for efficiently recovering or removing metal ions from solution.
In the plating of precious metals, such as gold and silver, much precious metal is lost in what is known as the drag out from the rinse solution. There are known techniques which are used to recover a portion of the precious metal from the rinse tank. These known techniques have the limitation that the amount of the precious metal recovered is limited so that much precious metal is lost. To put it another way, the value of the additional metal recovered does not warrant the cost of recovering substantially all of the precious metal in the rinse with the known techniques.
Accordingly, it is a major purpose of this invention to provide a technique for recovering metal from a rinse which is more efficient or more economical than are previously known techniques.
More specifically, it is a purpose of this invention to provide a metal ion recovery unit which is fairly inexpensive in construction and which, furthermore, is relatively inexpensive to operate.
Thus, it is a purpose of this invention to provide a metal recovery unit which is sufficiently efficient that it can be economically used to recover virtually all of the metal in a solution.
In addition to the value of the metal recovered from precious metal plating processes, there is the environmental need for recovery of metal in all types of metal finishing operations so that the metal, be it a precious metal or a base metal, is not flushed down into the sewers. Indeed, there are various legal requirements which many metal finishing operations have to meet to minimize the amount of metal flushed into the sewage system.
Accordingly, it is an important and related purpose of this invention to provide a metal ion removal system that can be adapted to use with a wide range of metals, both precious and base, so that the recovery unit can be used not only to recover valuable metals but also to remove metal from solution to minimize the pollution created by metal finishing plants.
In metal finishing operations, it is desirable that the metal recovery unit be as compact as possible. In general, space requirements in most metal finishing operations prohibit the use of a large recovery unit. Accordingly, it is another purpose of this invention to provide a compact metal recovery unit.
As indicated above, it is important that a metal recovery unit be as efficient as possible, as compact as possible and operate to recover as much of the metal as possible. But these three operating parameters are to some extent contradictory. For example, it is relatively inefficient to recover the last portion of the metal from a solution. Furthermore, a compact system tends to be less effective in the removal of metal. But there is usually a trade-off between these parameters.
Accordingly, it is a purpose of this invention to provide a metal recovery unit which has a structure and operating mode that not only optimizes the trade-off between these parameters but also makes the trade-off less critical so it is possible to provide substantially complete metal recovery while not sacrificing efficiency and compactness very greatly.